LO 10-7 Outline lubrication system maintenance and service procedures

1. Maintenance of Lubrication Systems

Maintenance of Lubrication Systems

While the properties of oil and the lubricating system can seem complex, the most common considerations for a technician are when and how to change the oil. A technician will need to diagnose problems with oil circuits, coolers, and control valves fewer times, but failing to service engine oil can dramatically shorten engine life and lead to catastrophic and costly component failures. Overservicing an engine is often viewed as an effective maintenance strategy, but the quantity of oil used during a service and the accompanying cost of replacing oil and filters too frequently is inefficient. It also yields few, if any, meaningful benefits compared to timely service intervals. Understanding the factors that limit oil life and the methods used to evaluate the optimal service schedule are the most helpful service recommendations technicians can provide when advising customers.

Other relatively common conditions encountered by technicians are situations where a customer reports high oil consumption and excess engine oil in the crankcase or low oil pressure. These conditions often point to potentially imminent engine failure, which can be prevented with diagnostic inspections and service interventions.

1.1. Limiting Factors to Engine Oil Life

Limiting Factors to Engine Oil Life

Today’s diesel engine technology requires that lubrication oils meet a variety of operating conditions and provide for long service intervals and engine durability. To understand what additives are needed to provide acceptable service, and when oil should be changed, it is helpful to consider the main factors that can limit oil life.

The Percentage of Solids
The percentage of solids refers to the total amount of particles that are suspended in the oil. Combustion soot, dirt, and oxidized oil are typically the major solids found in oil. The percentage of solids becomes a limiting factor to oil life when the particles interfere with the oil’s lubricating abilities. Engine manufacturers suggest an oil change to remove dissolved solids before they rise above 5% by weight. However, improvements in wear reduction are best achieved if the solids are kept below 2%. Detergents are added to the oil to prevent the solids from clumping and forming damaging deposits inside the engine. Detergents surround the particles and suspend them in the oil until it is drained or until the filter removes the particles. Synthetic oils require change intervals, just like conventional oils, if the percentage of solids is the limiting factor to engine oil life.

Sulfur and Combustion Acids
Sulfuric acids are formed in engine oil from two sources. One source is from sulfur in the diesel fuel, the other is from recirculating exhaust gases containing fuel-borne sulfur back into the cylinders. Because sulfur combines with the water produced during combustion, highly corrosive acids are formed in the oil. Additionally, oil oxidation can change the pH of oil. To counteract this condition, oil manufacturers add alkali or chemically based substances, such as calcium and ash, to the oil to neutralize the effect of sulfuric acids. The use of these additives distinguishes oils used in SI engines from oil used in diesel engines. The total acid number (TAN) refers to the acidity of an oil, whereas the total base number (TBN) is the measurement of a lubricant’s reserve alkalinity, which aids in the control of acids formed during the combustion process. The higher an oil’s TBN, the more effective it is in preventing the formation of wear-causing contaminants. Diesel engines will use a TBN of between 6–10 points. When the TBN is below half its new value, the engine oil should be changed.

Technicians Tip     The latest oil classifications for diesel engines are formulated to be compatible with the use of EGR and several different types of exhaust system catalysts. Sulfated ash, the additive once used to increase the TBN of diesel lubrication oil, is now almost eliminated. The removal of sulfur from fuel, as has occurred in recent years, is an important factor in extending the life of the catalyst material in the DPF. Less ash and other alkaline substances that can plug these catalysts are now used in engine oil. As the engine uses oil, the ash, which normally does not burn and, instead, deposits in the DPF, is now gone. As a result, the DPF requires fewer scheduled cleanings (not regeneration) when CJ-4 or CK-4 oil is used. Note that algorithms used by OEMs estimate ash loading of DPFs based on the use of the oil classification recommended at the time of engine manufacturing.     Oxidized Oil Oil is oxidized when it is exposed to air and oxygen combines with oil molecules. Conventional oils generally thicken, turn brown, and form deposits if highly oxidized. This process occurs more rapidly at high temperatures. The problem with oxidation is that oil loses some of its lubricating properties as it oxidizes, thus accelerating engine wear. Oxidation has shown strong correlations to lead corrosion in engine bearings. Synthetic oils are at an advantage because they do not oxidize as quickly as conventional oils. Measurements of oil oxidation during oil analysis are helpful because oxidation is the most sensitive and repeatable measure available of oil degradation. Therefore, if oil oxidation due to high engine operating temperatures is the limiting factor of oil life, the use of synthetic oil can extend the oil change interval. CK-4 oils have an improved additives package to limit oil oxidation Figure 54.

FIGURE 10-54: Oil chemistry changes depend on the type of driving cycle the vehicle encounters.

Other Oil Life-Limiting Factors
Engine problems, such as coolant leaks into the oil from sources such as leaking heads, require an oil change after a repair. Defective air filters that permit dirt to enter the engine, fuel leaking into the oil, wrong fuel (i.e., gasoline contamination of diesel fuel), water in the oil, or a mechanical failure producing internal debris are all circumstances that require an oil change subsequent to engine repair. Failing to change the oil has resulted in many engines experiencing catastrophic failures shortly following seemingly minor repairs.

When oil turns milky white, brown, or gray, it is usually a sign that coolant has leaked into it. Minor internal coolant leaks are not easily detected, and an oil sample should be obtained for analysis TABLE 10-6. Conventional antifreeze leaks will show up on an oil analysis as high silicate levels in the oil. Long-life antifreeze has other chemical signatures. Fuel contamination of oil can often be detected by simply smelling the fuel in the oil or performing an oil analysis after obtaining an oil sample.

1.2. Engine Oil Contamination with Biodiesel

Engine Oil Contamination with Biodiesel

For years biodiesel has been considered a fuel lubricity additive to keep moving parts operating smoothly inside fuel injection systems. The dilution of engine oil with biodiesel is another matter. Biodiesel promotes fuel dilution of engine oil to a much greater extent than mineral diesel fuel. Oil dilution with biodiesel occurs when a common rail fuel system uses a postcombustion injection of fuel into the cylinders to regenerate the particulate trap or NOx absorber. All the fuel is expected to vaporize in the cylinder and not combust until it reaches the exhaust catalysts. Heavier, less volatile fractions of fuel, however, do not vaporize during postcombustion injection, and liquid fuel clings to the cylinder walls before it is scraped into the crankcase.

Because biodiesel has a higher distillation temperature and boiling point, it does not burn away or boil out of engine oil. The result is a tendency to dilute the engine oil disproportionately to its blend ratio in the fuel. Biodiesel blends higher than B20 (20% biosource) cause larger amounts of unburned fuel to slip by the piston rings. Fuel passes by the pistons and accumulates in the crankcase. Once there, fuel polymerizes (joins together to form long, complex-shaped molecules) with oil, producing thick sludge. Engine damage can result from oil passageways being blocked by sludge. Deposits also form in the ring belt area, causing the rings to stick and crankcase blowby to increase, which further aggravates oil contamination with increased levels of soot.

Raw or refined vegetable oils produce the greatest harm, which may not become evident until a significant amount of damage has occurred over an extended period. Engine oil change intervals may need to be shortened significantly if using blends of biodiesel higher than B20. Note that detergents and specific antiwear additives do not work as well when oil is diluted with biodiesel either.

1.3. Oil Change Interval

Oil Change Interval Oil change intervals are based on the operating conditions an engine encounters and the amount of fuel consumed. Several formulas are used to calculate the correct service interval, but generally, every 45 gallons (170 L) of fuel consumed by the diesel engine produces enough contaminants to use up to 1 quart (1 L) of oil. The recommended oil change interval is calculated by multiplying the quantity of oil in the oil pan by the number of barrels of fuel burned (45 gallons [170 L]). This means a vehicle with 7 miles per gallon (mpg; 3 km/L) fuel consumption, with an oil pan capacity of approximately 40 L (close to 9 gallons), will need to be changed at 12,600 miles (20,117 km). Extending service intervals beyond this can be achieved using good-quality lubricating oils, such as synthetics, that resist oxidation and acid formation. Filters that remove oil life-limiting soot are also needed. An engine ECU can be configured to prompt the driver to have the engine oil changed. A maintenance monitor light in the dash can alert the driver when oil is at the end of its service life. Technicians need to reset the monitor after service Figure 55. Stop-and-go urban traffic, heavy loads, cold weather, extended idle, etc., are severe operating conditions that shorten the oil service interval. Moderate temperatures and steady-state driving conditions on a highway are normal service conditions that extend oil life TABLE 10-7. The best practice to extend oil change intervals is to use engine oil sampling analysis to determine the levels of solids, TBN, and limits of oil oxidation.

FIGURE 10-55: This Caterpillar engine has software that enables technicians to activate a dash light to alert the driver when a service is due.

1.4. Replacing a Spin-On Oil Filter

Replacing a Spin-On Oil Filter

Oil filters on diesel engines are changed every time the oil is changed. Unlike some gasoline-fueled, SI engines that can have the oil filter replaced during every other oil change, diesel engine oil filters load faster with contaminants and therefore require more frequent changing. The majority of contaminants in diesel engine oil are combustion byproducts, such as soot. Some manufacturers even recommend changing the oil filters between oil changes if a vehicle uses synthetic oil. More frequent filter changes help keep soot loading of oil low, which enables extended oil change intervals. Multiple spin-on filters with high contaminant-holding capacity require simple precautions during installation.

To replace a spin-on oil filter, follow the steps in Skill Drill 10-1.

1.5. SKILL DRILL 10-1  Replacing a Spin-On Oil Filter

STEP 1 With the engine off, remove the filter using a filter wrench. A large belt-type filter wrench assisted by a power bar can be used to remove a tight filter. Occasionally, chain-type belt wrenches are used to remove tight filters. To prevent hot oil from scalding your hand when the filter is removed, a hole may be punched into the bottom of the filter to allow oil to drain before removal. STEP 2 Visually inspect the filter base for any damage or warpage. Ensure that the old filter gasket is removed. STEP 3 Fill the new filter with oil. Pour oil in the unfiltered outer holes of the cartridge (the center filter hole returns filtered oil to the engine). STEP 4 Lubricate the filter gasket with oil or a smear of grease. This will help the gasket slide on the filter base and prevent the gasket from buckling when the filter is tightened. It is also necessary to lubricate the gasket to enable easy removal during the next service. STEP 5 Spin the new filter on hand tight. Note the arrows or markings at the top of the filter canister, which indicate how far the new filter should be tightened after snugging the filter to the base using hand force only. Most filters are tightened a quarter or half turn beyond hand tight. Tightening the filter further can potentially distort the filter base, which is often aluminum. The filter can also be damaged and internal leak paths formed if it is overtightened. If the filter is too loose, it will leak.     STEP 6 If the engine is being started for the first time after an overhaul, the engine should be pre-lubricated with pressurized oil through an oil gallery plug. As an additional precaution to prevent damage to bearings and other moving parts from oil starvation, disable the fuel system by disconnecting an ignition fuse or crank and cam sensor or by using a remote starter button. Crank, but do not start, the engine until oil pressure appears on the direct reading gauge in the instrument cluster. STEP 7 After the engine is started and oil pressure is stabilized, check for leaks. Reset any maintenance monitor to indicate when the next scheduled filter and oil service is required.

1.6. Measuring Oil Quality

Measuring Oil Quality
It is in the best interests of owners and the environment to extend oil change intervals. Owners are motivated to sample engine oil to determine if any oil properties are depleted and whether the oil need not be changed if oil properties are intact. Reduced operating costs are another benefit to oil sampling, as is the fact that important clues about impending engine failures can be detected before a catastrophic failure occurs.

From an environmental viewpoint, extending oil change intervals reduces environmental waste. According to the EPA, of the 1 billion gallons of engine oil consumed every year, about 185 million gallons (700 million L) of used engine oil are disposed of improperly. Likely, the oil is dumped into the ground, tossed into landfills, or poured into sewers. The EPA now encourages vehicle owners to follow the oil change recommendations of the OEMs and not those of the oil change industry. Research has demonstrated that oil changes can be extended by using higher-quality oil and oil analysis for HD diesels.